The invention relates to a low-pressure mercury vapor discharge lamp comprising a discharge vessel,
which discharge vessel encloses a discharge space provided with a filling of mercury and a noble gas in a gastight manner, PA1 electrodes being arranged in the discharge space for generating and maintaining a discharge in the discharge space, PA1 and an electrode shield at least substantially surrounding at least one of the electrodes.
In mercury vapor discharge lamps, mercury is the primary component for (efficiently) generating ultraviolet (UV) light. An inside wall of the discharge vessel may be provided with a luminescent layer comprising a luminescent material (for example a fluorescent powder) for converting UV to other wavelengths, for example UV-B and UV-A for tanning purposes (sun-couch lamps), or to visible radiation. For this reason, such lamps are also referred to as fluorescent lamps.
A low-pressure mercury vapor discharge lamp of the type mentioned in the opening paragraph is known from DE-A 1 060 991. In the known lamp, the electrode shield surrounding the electrode is made of titanium sheet. The use of an electrode shield, also referred to as anode shield or cathode shield, counteracts blackening at an inside wall of the discharge vessel. The titanium serves in this respect as the getter for chemically binding oxygen, nitrogen and/or carbon.
A disadvantage of the use of a metal or metal alloy is that it may cause a short-circuit of the pole wires of the electrode. In addition, the metals in the electrode shield may amalgamate with the mercury present in the lamp and, thus, absorb mercury. As a result, to obtain a sufficiently long service life of the known lamp, a relatively high mercury dose is necessary. If the lamp is unskilfully processed after its service life has ended, the environment is adversely affected.